The British owner of Citizens Bank plans to sell 20 to 25 percent of the bank to investors in roughly two years, a move expected to have little impact on depositors.

Royal Bank of Scotland is expected to announce Thursday, when it releases quarterly earnings, that it is planning to launch an initial public offering for its American subsidiary and sell a minority share of stock on public exchanges, according to a person briefed on the matter, but not authorized to speak publicly. Citizens, based in Providence, is the second-largest retail bank in Massachusetts and one of the largest in the United States.

The possible sale of a stake in Citizens was first reported by the Telegraph of London over the weekend. Royal Bank of Scotland declined to comment.

Royal Bank of Scotland has come under growing pressure from regulators and investors to sell Citizens to raise capital and help repay British taxpayers, who bailed out the bank during the global financial crisis. The British government still owns about 81 percent of the bank, headquartered in Edinburgh.

But its executives have fiercely resisted selling Citizens until now, saying the bank has bounced back from the financial crisis, earns a steady profit, and will probably be worth even more in a few years.

Potential buyers could include Canada’s Toronto-Dominion Bank, the parent of TD Bank, one of the largest regional banks in Massachusetts and the East. Toronto-Dominion declined to comment. Citizens has 1,400 branches in 12 states, including 254 in Massachusetts. It employs­ ­nearly 19,000 people, including about 3,400 in Massachusetts.

Financial analysts have estimated Citizens Bank is worth roughly $12 billion today, but might fetch more in a few years as the US economy recovers and more banks are in a position to make a bid. Royal Bank of Scotland has sold portions of its businesses to the public before. The bank recently floated 30 percent of an insurance unit and plans to sell the rest by 2014 at the behest of European bank regulators.